|Monte on Jul 3, 2003 at 1:33:33 PM (# 374)|
Yeah, I saw that episode...it was a pretty interesting episode.
MHenke on Jul 4, 2003 at 4:11:07 AM (# 375)
So, cdrom600, here we go again.
Why can photons move at speed of light?
The (well known) formular e=mc² describes the relation between mass and energy, but according to the theory of relativity the mass of a particle is relative to its speed, and m stands for that relative mass. The special case e0=m0c² describes the rest energy of an object (where m0 is its rest mass) and both are constant particle properties.
The relation between rest mass, relative mass and speed is represented by the (simple) formular m=m0/sqrt(1-v²/c²) that, if inserted into e=mc² leads to our known result that the energy of a particle grows to infinite if the speed of the particle nears the speed of light, or rephrased, it takes an infinite amount of energy to accelerate a particle at speed of light.
But that's valid only for particles that have a rest mass greater zero! And that's it. Photons have a rest mass of zero, although they actualy have a relative mass. And that's no discrepancy, since they don't exists in a state of rest, the speed fo light (and therefore the speed of photons) is constant.
Moreover, we can easily calculate the mass m of a photon. Since the energy e of a photon at a given frequence f could be calculated as e=h*f (where h is Plank's constant 6.625*10-34 J), we retrieve h*f = mc² and m=h*f/c²...
Example: A photon with a frequence of 10kHz has an energy
e = h*f = 6.625*10-34Js * 10000s-1 = 6.625*10-30J (J = m2kgs-2)
Inserted in e=mc², resolved to m=e/c² (c ~ 3*108 m/s)
m = e/c2 = 6,625*10-30 m2kgs-2/ 9*1016m2s-2 = 7.4*10-47kg
Well, that's quite lightweight, but it's more than nothing... :]
ChrisRickard on Jul 4, 2003 at 8:54:57 PM (# 376)
So does that mean as e->0 mass also -> 0???
Holophrastic on Jul 5, 2003 at 12:37:33 AM (# 377)
well, that's a round-about perspective, but yes.
e is a measure of an objects speed and of its mass -- its inertia/momentum/force. if it had no mass, it would have no energy, it would require no energy to move it, and it would require no energy to stop it. And since it has no energy, it wouldn't exist.
now of course, we flow between many ages of physics here, and surely the next one will disagree, but for now, that's the story.
look at things the other way -- every object is nothing more than a ball of energy. That energy can be in the form of mass, or a few other things. The objects we find familiar are of mass. And any energy required to move that mass now becomes part of that moving mass.
so if a ball is e=4 and you hit it with force 2 then the ball is now of e=6. when it stops, it will be 4 again.
Terry Young on Jul 5, 2003 at 10:35:43 AM (# 378)
This message has been edited.
Darn, I've missed it. Anyway, since the "damage" has been done, it wouldn't hurt to...
Terry Young on Dam 0, 0000 at 0:00:00 AM (# 400)
... try again... ^^
Interesting how this thread leads us to, btw...
And interesting if you look at Hol's post time compared to mine... and the order of the posts... we're bouncing back in time...
MHenke on Jul 7, 2003 at 1:34:40 AM (# 379)
>So does that mean as e->0 mass also -> 0???
Yep, that's a inevitable conclusion of e=mc². Colloquial rephrased, it says that mass and energie are equivalent, they differ just in a constant (c²). So, e->0 <=> m->0.
But, as said before, rest mass and rest energy of a particle are constant properties, so an arbitrary particle won't vanish if it "stops", that's valid only for particles that has a rest mass of zero...
(And of course, as Holo already insinuated, only if our universe actually follows the theory of relativity, nobody knows for sure, although by now it's a quite good model and there are several experimetal proofs...)
And Terry, from where you're posting? A spaceship with negative rest mass traveling at hyper speed of light?
im3dia on Jul 7, 2003 at 6:07:15 PM (# 380)
First of all "Hi to everybody!"
My opinion for the moment and I don't think it will change in the near future is that it is impossible to hide the source code... I don't really know why this thread has so many pages to tell you the truth!
However I have an interesting source code at http://www.interactivedia.com/encrypt/